1. Field of the Invention
The present invention relates to a reciprocatory piston type compressor for compressing a refrigerant gas, and more particularly, to a reciprocatory piston type compressor having a noise and vibration suppressed discharge valve mechanism.
2. Description of the Related Art
Many reciprocatory piston type compressors, such as a swash plate type compressor and a wobble plate type compressor are known. A typical swash plate type compressor having a reciprocatory piston-operated compressing mechanism for compressing a refrigerant gas is shown in FIG. 9. The compressor of FIG. 9 has a pair of axially combined cylinder blocks 1 and 2 which are closed at front and rear opposite ends thereof by a front and rear housings 5 and 6, via front and rear valve plates 3 and 4, respectively. The front housing 5, the front valve plate 3, the cylinder blocks 1 and 2, the rear rear valve plate 4, and the rear housing 6 are tightly combined together by a suitable number of screw bolts ( not shown ). The combined cylinder blocks 1 and 2 have a swash plate chamber 7 formed therein at a connecting portion thereof, and a swash plate 9 is arranged in the swash plate chamber 7 to be keyed on a drive shaft 8 extended through shaft bores 1a and 2a formed at the center of the combined cylinder blocks 1 and 2. The combined cylinder blocks 1 and 2 are provided with a plurality of axial cylinder bores 10 radially equidistantly arranged around the axis of the drive shaft 8 and axially extended in parallel with the center of the drive shaft 8. A plurality of double-headed pistons 11 are slidably fitted in the plurality of cylinder bores 10 to be engaged with the swash plate 9 via shoes 12, and are reciprocated by the swash plate 9 when the swash plate 9 is rotated together with the drive shaft 8.
The front and rear housings 5 and 6 are provided with outer suction chambers 13 and 14 for a refrigerant gas before compression, respectively, and inner discharge chambers 15 and 16 for the refrigerant gas after compression, respectively. The swash plate chamber 7 is fluidly connected to the suction chambers 13 and 14 via a suction passageway ( not shown ), and the discharge chambers 15 and 16 are fluidly connected to an external refrigerating circuit.
The front and rear valve plates 3 and 4 are provided with suction ports 17 and 18 fluidly connecting the suction chambers 13 and 14 to the cylinder bores 10, and discharge ports 19 and 20 fluidly connecting the cylinder bores 10 to the discharge chambers 15 and 16. The front and rear valve plates 3 are also provided with inner faces, respectively, confronting the cylinder bores 10 of the combined cylinder blocks 1 and 2, and covered with front and rear suction valve sheets having suction valves 21 and 22 which open and close the suction ports 17 and 18. The valve plates 3 and 4 are further provided with outer faces, respectively, confronting the front and rear housings 5 and 6, and covered with front and rear valve sheets having discharge valves 23 and 24 which open and close the discharge ports 19 and 20. Valve retainers 25 and 26 are arranged behind the discharge valves 23 and 24, respectively, to limit the opening of the discharge valves 23 and 24.
The front and rear discharge valves 23 and 24 are formed in such a manner that they are in close contact with marginal portions of the outer faces of the valve plates 3 and 4, surrounding the discharge ports 19 and 20, and therefore, when the pressure of the refrigerant gas in the cylinder bores 10 rises to a predetermined level due to compression by the reciprocating pistons 11, the discharge valves 23 and 24 are bent toward the respective valve retainers 25 and 26 to open the discharge ports 19 and 20 and thereby permit the refrigerant gas compressed in the cylinder bores 10 to be discharged toward the discharge chambers 15 and 16.
The above-described reciprocatory piston type compressor is supplied with a lubricating oil in the form of an oil mist suspended in the refrigerant gas, and thus, the oil mist is adhered to the end surfaces of the front and rear valve plates 3 and 4 and the surfaces of the front and rear discharge valves 23 and 24 in a manner such that the end surfaces of the front and rear valve plates 3 and 4, and the surfaces of the front and rear discharge valves 23 and 24, are always coated with an oil film. The end faces of the front and rear valve plates 3 and 4 also are provided with smooth surfaces having surface roughness between only 6 through 7 Rz so that, when the valve plates 3 and 4 are accommodated in the compressor between the axial ends of the cylinder blocks 1 and 2 and the front and rear housings 5 and 6, a complete air-tight condition between the high pressure region, e.g., the discharge chambers 15 and 16 and the low pressure region, e.g., the suction chambers 13 and 14, is achieved without an occurrence of a fluid leakage via the surfaces of the valve plates 3 and 4, to thereby obtain a high volumetric efficiency in the compression of the refrigerant gas. Namely, if the surface of the end faces of the valve plates 3 and 4 is rough, an oozing of the high pressure refrigerant gas from the high pressure region to the low pressure region via the rough end faces of the valve plates 3 and 4 occurs, due to a pressure differential between the high and low pressure sides, and therefore, the volumetric efficiency in the compression of the refrigerant gas is lowered.
Nevertheless, when the surface of the end faces of the valve plates 3 and 4 are smooth, the discharge valves 23 and 24 of the valve sheets are brought into tight contact with the end face of the valve plates 3 and 4 during the closing of the discharge ports 19 and 20, due to a surface tension exhibited by the oil film coating the valve plates 3 and 4. Accordingly, during the operation of the compressor the discharge valves 23 and 24 of the valve sheets are not separated from the end faces of the valve plates 3 and 4, to open the discharge ports 19 and 20, until the refrigerant pressure in the cylinder bores 10 rises to a pressure level sufficient to overcome the surface tension and the adhesive force of the oil film, and therefore, an excessive compression occurs in each of the cylinder bores 10. Thus, when the discharge valves 23 and 24 are opened under such an excessive compression of the refrigerant gas in the cylinder bores 10, the compressed gas bursts out of the cylinder bores 10 into the discharge chambers 15 and 16, and the ends of the opened discharge valves 23 and 24 violently collide with the valve retainers 25 and 26. Therefore, the compressor and the surrounding mechanisms generate an undesirable pulsive vibration and noise.
To overcome the above-mentioned vibration and noise problems encountered by the conventional reciprocatory piston type compressor, the present assignee company has already made several proposals. For example, U.S. Pat. No. 4,781,540 to Ikeda et al discloses an asymmetric valve mechanism for a piston type compressor. Nevertheless, the present inventors have continued their experiments, to obtain a less costly method of solving the above-mentioned problems, and accordingly, experimented with a roughening of the end faces of the valve plates at particular portions surrounding each of the discharge ports and coming into contact with the discharge valves, to prevent the above-mentioned tight contact between the discharge valves and the valve plates. As a result, the occurrence of an excessive compression of the refrigerant gas in the cylinder bores could be reduced, and therefore, the noise and vibration were suppressed. Nevertheless, it was found that, when the discharge valves 23 and 24 repeatedly collide against the valve plates to close the discharge ports of the valve plates 3 and 4, the roughened portions of the end faces of the valve plates 3 and 4 are gradually abraded and become smooth, and accordingly, the excessive compression of the refrigerant gas in the cylinder bores 10 gradually reoccurs. Namely, it is difficult to prevent the occurrence of the excessive compression of the refrigerant gas in the cylinder bores 10 after a long time usage of the compressor.